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This configuration puts the fuel tank in the middle of the CG range along with the extra seat. As the fuel burns off, the flight characteristics of the airplane do not change. Furthermore, as the aircraft loading increases with a passenger or passenger seat bag, the CG stays in the safe range.

This configuration puts the fuel tank in the middle of the CG range along with the extra seat. As the fuel burns off, the flight characteristics of the airplane do not change. Furthermore, as the aircraft loading increases with a passenger or passenger seat bag, the CG stays in the safe range.

Bob Wilson

Ah....that just doesn't seem like the safest choice. That was actually one of the first structural choices I made in designing both of the aircraft I have worked on so far. Both of them have well protected fuel tanks in the wings.

How much stroking distances do you have under the seats just out of curiosity?

Unfortunately in science what you believe is irrelevant.

"I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.

Steve, it's actually a pretty common solution for earlier designs of light aircraft - a bunch of WWI era planes had the tank under the seat for CG/maneuverability concerns.

Different question - would one need a glass panel for the USB data recorder to work, or could a small data collector box be made to support it for us Standard Six guys, with a little GPS receiver like the ones that plug into an iPad?

Mr. Wilson is right on the money with the flight testing goal - one of my concerns in the First Forty is being able to juggle recording information while flying what will undoubtably be a handful of an aircraft (short taildragging biplane). I sure would be nice to work out Vx and Vy info on a desktop computer after the fact, and to see precisely the stall speeds as well as temps.

The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

. . .
Different question - would one need a glass panel for the USB data recorder to work, or could a small data collector box be made to support it for us Standard Six guys, with a little GPS receiver like the ones that plug into an iPad?

Curious you mention the iPad. I have a Dual GPS-to-bluetooth receiver that works with the iPad. The sad news is I have not found 'track recording' app to record a trace. In contrast, the nuvi GPS receivers keep a track record that can be downloaded to a computer. But it is easier to just get a GPS 'mouse' connected to a laptop and stream the data to a file ... which could be on the USB stick.

In my Prius energy studies, I used a GPS mouse to calculate the kinetic and potential energy which I could correlate with OBD data from the engine. This gave me a total vehicle energy model to refine Prius operations.

Originally Posted by Frank Giger

. . .
Mr. Wilson is right on the money with the flight testing goal - one of my concerns in the First Forty is being able to juggle recording information while flying what will undoubtably be a handful of an aircraft (short taildragging biplane). I sure would be nice to work out Vx and Vy info on a desktop computer after the fact, and to see precisely the stall speeds as well as temps.

In my case, I had decided to replace the existing electro-mechanical instruments with MEMS based systems. This substantially improves reliability and accuracy. I was pleased to find it also comes with an RS-232, external data logging capability. But there is one thing I had not expected, increased interior volume.

This is the current cockpit, pilot's side:
Everything to the left of the Nav/Com goes including the panel and this becomes the access way for maintenance. In the remaining column, there will be the flight director, com radio, engine monitor, and throttle. It will also have a set of switches and electrical power monitors.

The pilot side rudder pedals and brakes will be moved forward about 4-6" while the passenger side pedals will optionally fold down. Short pilots are checked out in the right seat and longer legged ones in the left. All flight, engine, and power controls and instrumentation are in the center console for shared access.

I may move the center console stick to the left, it already has a passenger side stick. This makes it easier to mount any additional switches on the shared console space . . . and install the cup holders.

If you want to record the six-pack, you must make them electronic first, unless ... Video actually works well, and you get 30 frames/second. Plus, you can record comments, too. For certification, we actually use video to determine electronic airspeed lag (yes, steam gauges (pneumatic instruments) actually have less lag than electronic instruments (PFDs) due to A-D converters and data buses).

The whole, inexpensive FDR concept is a GREAT idea. Record every data bus you can. There is a really cool program called LabView (by National Instruments) that has changed the flight test world as an "inexpensive", PC-based, few parameter recording tool. All data is good data.

As a word of caution, GPS data has drawbacks, but it will get one in the ballpark. Know how often the data is being output and the accuracy of that data. The flight test industry uses differential GPS and then time corrects that information.

I hadn't thought to check the response time of MEMS based instruments. Do you use hot-wire anemometers as the reference to check the delay and accuracy?

Originally Posted by Ron Blum

. . . There is a really cool program called LabView (by National Instruments) that has changed the flight test world as an "inexpensive", PC-based, few parameter recording tool. All data is good data.

You're right about the quotes! But I pretty much just use excel.

Originally Posted by Ron Blum

. . . As a word of caution, GPS data has drawbacks, but it will get one in the ballpark. Know how often the data is being output and the accuracy of that data. The flight test industry uses differential GPS and then time corrects that information.

The first 10 minutes or so, the GPS data wanders all over the place and the altitude data is worse. But after 10-15 minutes it settles down . . . or wanders less. Still, I'm curious about differential GPS.

When I was picking up N19WT, signing the final papers, a Cessna flew in through a drizzle, 40F, 500 ft. ceiling, and 20+ Kt wind. I know because I was loading the plane on the trailer that wet, miserable day. The pilot said he used a GPS approach. Still, I started looking at the WAAS and I see it covers large areas. I have GPS receiver options with the flight system so I'll see if any of them incorporate WAAS capability or the other systems without costing an arm and leg.

I'm a Day/Night VFR pilot and have no interest in IFR flight but I'm a firm believer in bi-annual, instrument training with emphasis on recovery from unusual attitude and being 'talked down.' I don't take off into known IFR weather but there are places between weather stations where only God and the pilot knows what is there.

Do you use hot-wire anemometers as the reference to check the delay and accuracy?

I'll keep this as generic as I can, but if you want more information, just email me.

First, we calibrate the boom, airborne and on the ground ... the two calibrations are significantly different (and may differ with configuration/flap/gear/etc. changes, too). Booms are known for being INaccurate, but highly repeatable. Then we do an easy one to one comparison to the different aircraft systems.

For delay we use an analog transducer sampled at a very high rate (250+ samples/sec). We also do "balloon burst" tests. For accuracy we calibrate each individual transducer (leaving only repeatability) and run several different flight tests, some using GPS for enhanced accuracy.

Originally Posted by bwilson4web

You're right about the quotes! But I pretty much just use excel.

LabView is a PC-based program that allows you to excite and record instrumentation without a full-blown data system. We use a version of "Excel" for data analysis. too.

Originally Posted by bwilson4web

The first 10 minutes or so, the GPS data wanders all over the place and the altitude data is worse. But after 10-15 minutes it settles down . . . or wanders less. Still, I'm curious about differential GPS.

OEMs use a couple forms of Differential GPS (DGPS). One is a service out of Canada that transmits the error (I'll explain that shortly ... and it costs), and the other (more accurate) is self-contained but requires two GPS units. You are exactly correct in that the GPS signal settles down ... but only while the unit is not moving). Explaining the 2-unit DGPS, one unit is in the airplane (moving), and the other unit is on the ground (fixed). Since the ground unit is not moving, the error is the difference in where the unit thinks it is versus the fixed (known) location. The error can either be post-processed or transmitted up to the airplane. The Canadian service works the same way but is a little less accurate. To put these accuracies in perspective, the Canadian service is within 2 meters I believe. The 2-unit system is within 2 centimeters.

The recent issue of "Soaring" magazine has a really good article on how GPS/DGPS works.

It has always amazed me how little panicked screaming there is on CVRs. Fair amount of cussing but it's a real testament to the pilots who handle the aircraft disasters caught on tape that they can maintain some semblance of a level head in situations like that.

The whole, inexpensive FDR concept is a GREAT idea. Record every data bus you can. There is a really cool program called LabView (by National Instruments) that has changed the flight test world as an "inexpensive", PC-based, few parameter recording tool. All data is good data.

But not necessarily valid data as pointed out by your next comment.

I'm a Day/Night VFR pilot and have no interest in IFR flight but I'm a firm believer in bi-annual, instrument training with emphasis on recovery from unusual attitude and being 'talked down.' I don't take off into known IFR weather but there are places between weather stations where only God and the pilot knows what is there.

The problem is that a biennial instrument review is of little use to most people since the retention rate of the skills is generally pretty dismal. One can often pretty readily correlate the frequency of loss of control/spatial disorientation events in instrument-rated pilots by looking at their total instrument time and even more so the amount accrued within the past 30 to 90 days. Relying upon being instrument rated and having infrequent reviews is going to create a false sense of security in many people.

Unfortunately in science what you believe is irrelevant.

"I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.

1A. (Good or bad) A lot of early (true) ultralights had fuel tanks that were designed as seats to save weight (to meet the 254 lbs. limit), but most were open cockpit with easy bailout capability. As time progressed (and as the "heavy" ultralights came into being), the fuel stayed there, but it got harder to get out of the vehicle. Remember what an ultralight's gross weight stall speed is supposed to be, though.

1B. Also look at a lot of the early light planes (yes, type certificated). The Champs, Cubs and Taylorcrafts all had header tanks. So, if the crash were nose down, the hot engine would be pushed back into the fuel tank. We have learned from these experiences, but as the saying goes, "The FARs are written in blood."

2. Bob has pointed out his limitations (and is conservative in a good way), which is the correct way to handle safety. You would be shocked at how many of the VFR into IFR condition fatalities happen to current, instrument rated pilots. The pilot (although rated) isn't ready for the transition, and it kind of freaks them out when they go IFR. If you don't believe me, I can tell you the "rest of the story" offline.